1. Field of the Invention
The present invention relates to a method of manufacturing a magnetic head used for writing data on a recording medium, and to a magnetic head substructure used for manufacturing the magnetic head.
2. Description of the Related Art
For magnetic read/write devices such as magnetic disk drives, higher recording density has been constantly required to achieve a higher storage capacity and smaller dimensions. Typically, magnetic heads used in magnetic read/write devices have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter referred to as an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate.
For read heads, MR elements in practical use include GMR (giant magnetoresistive) elements utilizing a giant magnetoresistive effect, and TMR (tunneling magnetoresistive) elements utilizing a tunneling magnetoresistive effect.
Write heads include those of a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and those of a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. Recently, the shift from the longitudinal magnetic recording system to the perpendicular magnetic recording system has been promoted in order to achieve higher recording density of magnetic read/write devices.
For each of the longitudinal magnetic recording system and the perpendicular magnetic recording system, the write head typically includes a coil for generating a magnetic field corresponding to data to be written on the recording medium, and a pole layer for allowing a magnetic flux corresponding to the magnetic field generated by the coil to pass therethrough and generating a write magnetic field for writing the data on the recording medium. The pole layer includes, for example, a track width defining portion including a first end located in a medium facing surface and a second end located away from the medium facing surface, the track width defining portion having a width that defines the optical track width, and a wide portion having a width greater than that of the track width defining portion and coupled to the second end of the track width defining portion. Here, the length of the track width defining portion taken in the direction perpendicular to the medium facing surface is called neck height. The neck height has an influence on the characteristics of the write head. In general, as the neck height gets smaller, magnetic flux of greater magnitude is allowed to be introduced to the medium facing surface through the pole layer, and as a result, the overwrite property, which is a parameter indicating overwriting capability, improves. If the neck height gets too small, however, the effective track width gets too great, which results in noticeable occurrence of problems such as a phenomenon in which, when data is written on a certain track, data stored on a track adjacent thereto is erased (this phenomenon is hereinafter called adjacent track erasing), and unwanted writing between two adjacent tracks. Under the circumstances, when manufacturing magnetic heads it is required that the medium facing surfaces be formed so that the neck height is of a desired value.
An example of a method of manufacturing a magnetic head will now be described. In the method, first, components of a plurality of magnetic heads are formed on a single substrate (wafer) to thereby fabricate a magnetic head substructure in which pre-head portions that are to become the respective magnetic heads later are aligned in a plurality of rows. The substructure includes a plurality of magnetoresistive films (hereinafter referred to as MR films) that are to be lapped later to thereby become the MR elements. Each of the MR films has such a shape that the length taken in the direction perpendicular to the medium facing surface is greater than the length of the MR element and that the width is equal to the width of the MR element. Next, the substructure is cut into a plurality of head aggregates each of which includes a plurality of pre-head portions aligned in a row. Next, a surface formed in each head aggregates by cutting the substructure is lapped to thereby form the medium facing surfaces of the pre-head portions included in each head aggregate. At this time, the MR films are lapped, so that the length thereof becomes a predetermined length and the resistance value thereof becomes a predetermined value, and as a result, the MR films become the MR elements. Next, flying rails are formed in the medium facing surfaces. Next, each head aggregate is cut so that the plurality of pre-head portions are separated from one another, whereby a plurality of magnetic heads are formed.
An example of a method of forming the medium facing surfaces by lapping the head aggregate will now be described. In the method, a plurality of sensors are provided in advance on the substructure, each of the sensors being formed of a resistor layer whose resistance value changes with changing amount of lapping when the head aggregate is lapped later. The resistance value of each of the sensors has a correspondence with the resistance value of the MR element. When the head aggregate is lapped, lapping is performed while detecting the resistance values of the plurality of sensors so that the resistance value of each of the plurality of sensors becomes a predetermined value. As a result, the medium facing surfaces are formed such that the resistance value of each of the plurality of MR elements is equal to the target value and that each of MR heights is equal to the target value. The MR height is the length of the MR element taken in the direction perpendicular to the medium facing surface.
According to conventional methods of manufacturing magnetic heads, the substructure is fabricated such that there is a certain positional relationship between the MR film and the pole layer. Therefore, ideally, if the medium facing surfaces are formed such that the MR heights are of a specific value, neck heights also become uniform. In actuality, however, since the MR film and the pole layer are formed in different steps, there arise variations in positional relationship between the MR film and the pole layer. Furthermore, even if the medium facing surfaces are formed while detecting the resistance value of a sensor having a correspondence with the resistance value of the MR films so that the MR heights are each equal to their target value, the neck heights do not always become equal to their target value. Consequently, according to the conventional methods of manufacturing magnetic heads, there may arise variations in neck height.
Conventionally, in the case of write heads of the longitudinal magnetic recording system, when the recording density is low, variations in neck height do not exert great influences on the characteristics of the write head. However, as the recording density increases, variations in neck height exert greater influences on the characteristics of the write head. In the case of write heads of the perpendicular magnetic recording system, variations in neck height exert greater influences on write characteristics, compared with write heads of the longitudinal magnetic recording system. Because of the foregoing, it has been required recently to reduce variations in neck height so as to obtain desired write characteristics.
To cope with this, as disclosed in JP 2006-048806A and JP 2006-073088A, it has been proposed to provide a sensor for controlling the neck height as well as a sensor for controlling the MR height on a substructure to thereby form the medium facing surfaces such that both of the MR height and the neck height achieve their respective desired values. In this connection, JP 2006-048806A mentions that throat height here means length from the air bearing surface to the point (flare point) at which the width of the track width portion of the main pole begins to widen. The “throat height” mentioned in JP 2006-048806A therefore actually means neck height.
JP 2000-251222A discloses a technique of providing a plurality of elements for monitoring the amount of lapping on a substructure to control throat height, so as to form the medium facing surfaces such that a desired throat height can be obtained.
A parameter that depends on the position of the medium facing surface and that has an influence on the characteristics of the write head is not limited to neck height. For example, throat height mentioned above is also such a parameter. If the values of such a plurality of parameters respectively depend on the positions of different portions to be determined in different steps, there arise variations in mutual relationship between the plurality of parameters. Consequently, for example, even if the medium facing surfaces are formed such that the neck height achieves its desired value, parameters other than neck height will not always achieve their desired values. When there arise variations in mutual relationship between the plurality of parameters, it is impossible to form the medium facing surfaces such that all of the parameters always achieve their desired values, because the values of the plurality of parameters each depend on the position of the medium facing surface. In such a situation, if a lot of magnetic heads are manufactured such that a desired value is achieved for only one of the parameters, such as neck height, magnetic heads falling out of spec due to significant deviation of other parameters from their desired values increase in ratio to all of the magnetic heads manufactured, and the yield of the magnetic heads thus decreases.